“Let’s go!” the Tonight Show host shouts, waving his arm above his head as a jukebox blasts “Runaround Sue.” “Shots for everyone!”

“He knows the owner of the bar,” our spy, Richie Alexander, explains of why Fallon was behind the bar. “I tried to buy him a shot, but he says he doesn’t do shots, so I bought him a beer,” said Alexander, who captured Fallon’s antics on video.

“I guess so many other people were offering to buy him a shot, that he just bought the whole bar a shot of vodka.”

Alexander, 23, of Williamsburg, says he had such a good time he can’t quite remember what bar it was.

“We just walked in off the street,” he explained. “It was somewhere around 23rd and 10th.”